This invention relates to magnetic head transducers and in particular to a magnetic head transducer having a transducing gap formed therein.
In recording or reading information on a moving information storage media, such as a magnetic recording disc, relative motion between a magnetic head transducer used for reading and writing information on the storage media on which information is written on and read from is required. The relative velocity between the head and media interface may be, for example, 550 IPS for video and high density digital applications. To achieve maximum performance, an interface of intimate contact is provided between the head and media surface without destruction or excessive wear of the magnetic flux-responsive coating on the surface.
As contact pressure between the head and media is increased to improve performance, both media and head wear are increased. The problem is particularly severe in video applications and compounded with the medias utilized for storing single video frames on separate tracks of a magnetic disc wherein one track at a time is continuously in contact with the head to provide a continuous stationary display of a single frame. In only five minutes of playtime revolving at 3,600 RPM, for example, a track on the disc is scraped about 18,000 times by the head; the by-products are so hard and abrasive that the same materials are commonly used as lapping compounds.
To prevent failure caused by contact between the head and disc, lubricated surfaces and/or air film separations have been used. However, any separation between the head and disc caused by such lubrication fluid or air film imposes a loss of signal and hence performance. A head/disc separation equal to one wave length could cause about 54.6 dB loss in the output of the replay head. Since it is desired to record wave lengths that approach 1.75 microns, the playback head voltage is reduced to 50% by only 0.19 micron of separation. On the other hand, as discussed above, reduction of separation to meet desired performance would cause the interface to be destroyed within a few seconds.
Prior art solutions to the head-to-disc interface problem have generally been of two types: flying heads in conjunction with rigid hard-surface discs and heads having large surface areas buried in soft flexible "floppy" discs. Flying head discs are very expensive and require complicated and expensive recording/playback systems. A flexible or so-called "floppy" disc reduces the handling and cost problems realized in the flying head rigid-disc systems. Some record/read heads for "floppy" discs are relatively large to provide an interface comprised of a large contoured head buried in the soft flexible media. The large record/read head surface area distributes the force per unit area to reduce media wear and separation loss. As the media is moved past the head, however, air collects between the head and disc surface to form an air film. The thickness of this air film is a function of head and media surface finishes, media stiffness, head-media penetration, head size, head surface contour, viscosity of the air and disc-head relative velocity. Because of these restraints, most flexible or "floppy" disc applications are limited to slow speed, low bandwidth digital computer applications or voice recording systems.
High performance head transducers for writing information on and reading information from a recording disc are generally formed by joining two magnetic pole pieces together with a transducing gap of finite length and width formed therebetween. The length and width of the gap are critical to head performance. In high density recording systems where track widths are typcially narrow (i.e., for example, 0.254 mm or 10 mils), relatively thin head transducers with narrow gaps are needed for effective system performance. This has the disadvantage of reducing the thickness of the bonding material which holds the two pole pieces together, thereby weakening the bond therebetween. The weakening of the bond by mechanical stress on the head transducer has the effect of altering the dimensions of the gap and producing non-uniformities in the width thereof. In copending patent application Ser. No. 749,954, now abandoned, assigned to the assignee of the present invention, a magnetic recording/playback head is described, wherein improved performance is achieved by beveling the upper portion thereof to form a thin, wedge-shaped upper portion while the base portion is thicker to enhance the mechanical strength of the head transducer and provide a stable gap configuration. The present invention relates to an improved technique for providing a head with a stable gap configuration and uniform gap dimensions while maintaining a thin head configuration.